Low-temperature autoclaves



July 26, 1955 R. JEWELL 2,713,702

LOW-TEMPERATURE AUTOCLAVES Filed April 17, 1953 Flcll ThermastatINVENTOR United States fiatent G 2,713,702 row-TEMPERATURE AUToc'LAvEsRaymond L. Jewell, Erie, Pa., assignor to American Sterilizer Company,Erie, Pa., a corporation of Pennsylvania Application April 17, 1953,Serial No. 349,489

6 Claims. (Cl. 21-98) This invention is intended to produce alow-temperature, moist-heat autoclave which will maintain within theautoclave chamber a uniforrrr controlled temperature below 212 degreesF. without creating a vacuum. Such autoclaves are useful in treatingheat-coagulable media such as bacteriological slants and inpasteurization of heat-sensitive solutions such as alkaloids,anaesthetics, proteins, vaccines, and serums. Such autoclaves are alsosubstitutes for the laboratory inspissator and are useful in laboratorywork requiring constant temperature and humidity. In a preferred form,the chamber is provided with a condenser and high pressure steam jetsare used to circulate the air and steam vapor so as to preventstratification. The condenser creates a sufiicient demand for steam so athermostatic control calls for steam injection a sufficiently large partof the time to maintain the 3-.

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is controlled by a thermostat 16 arranged in a fitting 17 leading fromthe line 12 adjacent the drain 13. A drain line 18 leading from thelower part of the line 12 through a check valve 19 conducts condensateto a suitable drain 20. The check valve serves as a restriction limitingbackflow of air from the drain when the aspirator produces a suction inline 12.

The manner in which the thermostat 16 controls the temperature withinthe chamber 1 is diagrammatically indicated in conjunction with thesolenoid valve 6. The valve 6 is normally closed and its solenoid 21 isconnected in series with the thermostat 16 to the power supply 22. Whenthe thermostat 16 cools below the temperature for which it is set, itcloses a contact 23 completing a circuit to the solenoid 21 which opensthe valve 6 and causes the injection of a high-pressure steam jet intothe aspirator 4. As the temperature of the thermostat 16 rises to theset value, it opens the contact 23 interrupting the circuit to thesolenoid 21 and permitting the closure of the valve 6 to cut off thesteam jet. The thermostat 16 'will ordinarily be adjustable throughout arange of from 150 degrees F. to 212 degrees F. and in the lower part ofthe range, e. g. 150-174 degrees will hold the temperature within thechamber to plus or minus 5 degress and in the upper part of the range174-212 degrees F. will hold the temperature within plus or minus 2degrees F.

The thermostatic control arrangement above described provides for theinjection of high-pressure steam to the aspirator 4 whenever thethermostat 16 calls for heat and shutting oft the flow of steam wheneverthe thermostat 16 is satisfied. This inherently results in intermittentsteam side elevation of an autoclave and Fig. 2 is an end view to ahigh-pressure steam line 5 controlled by a solenoid valve 6 and a manualvalve 7. The high-pressure steam line 5 has a discharge nozzle 8directed into the throat of a venturi nozzle 9 extending through theback wall 10 of the sterilizer chamber and having its inner or dischargeend 11 directed toward the front end of the sterilizer chamber. A line12 leading from a drain 13 at the lower front end of the sterilizer isconnected to the aspirator behind the steam jet discharge nozzle 8 sothat the jet of 1 steam discharged through the nozzle 8 into the venturitube 9 induces a flow of air and steam from the lower front part of thesterilizer chamber through the line 12 and into the aspirator. Thisproduces a flow of steam and air from the back toward the front of thesterilizing chamber as indicated by the arrows. In some cases, the loadwithin the chamber may sufiiciently distribute the flow of air and steamso that uniform temperatures will be obtained without stratification. Inother cases, it may be necessary to arrange a baflle 14 in front of thesteam jet with suitable openings 15 so directing the discharge from thefront end 11 of the venturi nozzle 9 so as to produce the desiredcirculatory flow within the sterilizing chamber. The high-pressure steamjet discharged through the venturi nozzle 9 produces a suction whichdraws the mixture of air and steam vapor from the lower front part ofthe chamber through the drain opening 13 and back to the aspirator 4through the line 12. This produces the desired circulation which isnecessary to maintain uniform temperature throughout the sterilizingchamber without stratification. The temperature within the sterilizingchamber injection, but unless some arrangement is provided fordissipating heat from the chamber 1, the intermittent steam injectionwill take place at intervals spaced too far apart to maintain uniformtemperature throughout the chamber. In order to cut down the intervalsbetween steam injection, a condenser is associated with the chamher 1cooling the vapor within the chamber so that more frequent steaminjection will be required. The condenser may be the jacket 2 in whichcase a water inlet line 24 is connected to. the back part of the jacketthrough a valve 25 and a water outlet line 26 is connected to the frontpart of the jacket through a line 27. The condenser may be in the formof a coil 28 (Fig. 2) having an inlet line 29 controlled by a valve 36and an outline line 31. Both condensers may be used together tosupplement each other. Other condensing arrangements are possible, itmerely being necessary that heat be taken away from the chamber 1 atsuch a rate that the intermittent steam injection to the aspirator 4will occur at such frequent intervals that Stratification within thechamber is prevented. Ordinarily, uniform temperature throughout'thechamber will be obtained if the steam injection takes place as little as25% of the time. There, of course, may be variations due to the size andtype of load within the chamber.

The low-temperature autoclave serves as a laboratory inspissator, whichis useful in the processing of heat-coagulable bacteriological slants,in the pasteurization of sterilization of various heat-sensitivesolutions such as alkatreated. Since the pressure within the chamber isalways above atmospheric pressure and the circulation necessary toprevent heat stratification is through the return line 12, there is nodanger of contamination by leakage of outside air into the chamber. Thehigh-pressure steam (15-30 pounds) injected to the aspirator 4 islikewise sterile. Better circulation throughout the chamber 1 isobtained by the intermittent shots of high-velocity steam than would beobtained with the same amount of steam steadily admitted under lowervelocity.

The autoclave produces a mixture of air and steam having a pressureequal to or slightly in excess of atmospheric pressure and a temperaturecontrollable to be substantially below the steam temperaturecorresponding to the chamber pressure. The condensate drain line, whichdischarges to atmosphere, prevents the creation of a vacuum in thechamber which would lower the boiling point of liquids or gels beingtreated.

It will be noted that for any selected temperature, the frequency of theintermittent steam injection will be directly related to the condensingwater rate after the chamber has come up to temperature. If theintermittent steam injection were at a fixed frequency, the condensingwater would control the temperature. Also, for a fixed condensing waterrate, changes in the frequency and duration of the steam injectionpulses Will also control the temperature. The thermostatic controlillustrated is, however, the simplest and most direct control of thechamber temperature. With the thermostatic control, the only adjustmentnecessary is an occasional change in the condensing water rate,increasing the water rate if the intermittent steam injection drops tosuch a low frequency that stratification would take place within thechamber and decreasing the water rate if steam is being wasted by toomuch steam injection. The Water rate need not be precisely adjusted.Satisfactory results are obtained if steam is injected 25% of the time.While the temperature will be maintained if steam is injected 100% ofthe time, this will be wasteful both of steam and water.

What is claimed as new is:

1. An autoclave comprising a chamber, a super atmospheric steam linedischarging into the chamber, means for circulating the steam within thechamber to prevent stratification, a valve controlling the admission ofsteam, a thermostat responsive to the chamber temperature and adapted tobe set for a temperature substantially less than the super atmosphericsteam temperature controlling the valve to open the valve when thethermostat calls for heat and to shut the valve when the thermostat issatisfied, and a condenser in heat exchange relation to the chamberadapted to cool the chamber while the thermostat controls the steamadmission.

2. An autoclave for producing a mixture of air and steam having apressure substantially atmospheric and temperature lower than the steamtemperature corresponding to the autoclave pressure comprising achamber, a drain from the chamber to atmosphere, a super-atmosphericpressure steam line discharging into the chamber, means for circulatingthe steam within the chamber to prevent Stratification, and a condenserin heat exchange relation to the chamber adapted to cool the chamberwhile the chamber is being heated by steam to prevent the rise oftemperature within the chamber to the temperature of steam atatmospheric pressure by heating from the steam discharge.

3. An autoclave for producing a mixture of air and steam having apressure substantially atmospheric and temperature lower than the steamtemperature corresponding to the autoclave pressure comprising achamber, a steam jet aspirator discharging into the chamber, asuper-atmospheric pressure steam line discharging into the aspirator, areturn line from the chamber to the aspirator, a drain from the chamberto atmosphere, a condenser cooling the chamber to create a demand forsteam, a thermostat responsive to the chamber temperature, a valve inthe steam line controlled by the thermostat shutting off the flow ofsteam to the aspirator as the thermostat is satisfied and opening thevalve when the thermostat calls for heat.

4. An autoclave for producing a mixture of air and steam having apressure substantially atmospheric and temperature lower than the steamtemperature corresponding to the autoclave pressure comprising achamber, a drain from the chamber to atmosphere, a steam jet aspiratordischarging into the chamber, a super-atmospheric pressure steam linedischarging into the aspirator, a bafile directing the aspiratordischarge so as to produce uniform circulation throughout the chamber, asuction passage leading from the chamber to the aspirator, a condensercooling the chamber to create a demand for steam, a thermostatresponsive to the chamber temperature, and an on-ofl valve in the steamline controlled by the thermostat.

5. An autoclave comprising a chamber, means for intermittentlydischarging jets of super atmospheric pressure steam into the chamber tomaintain a circulation of the atmosphere within the chamber to preventStratification, and a condenser in heat exchange relation to the chamberadapted to cool the chamber while the chamber is being heated by steamto prevent the rise of temperature within the chamber to the temperatureof steam at atmospheric pressure by heating from the steam discharge.

6. An autoclave producing a mixture of air and steam having a pressuresubstantially atmospheric and temperature lower than the steamtemperature corresponding to the autoclave pressure comprising achamber, a drain from the chamber to atmosphere, a steam jet aspiratordischarging into the chamber, a super-atmospheric pressure steam linedischarging to the aspirator, a suction line leading to the aspiratorfrom a point within the chamber remote from the aspirator discharge, anintermittently operated on-oif valve in the steam line, and a condensercooling the chamber during the period of intermittent operation of thevalve.

References Cited in the file of this patent UNITED STATES PATENTS2,082,460 Omsted June 1, 1937 FOREIGN PATENTS 227,267 Switzerland Aug.16, 1943 504,724 Germany Aug. 15, 1930

